Rep Power: 0

I just did a swap on my civic with the same motor but just from the 2004 civic. Swapped everything over. EGR, ignition switch and wire harnesses. Car is acting really weird. It's running terribly bad and it keeps sputtering and it's hard to start. It will start up when it's cold but when it's hot it sputters and stuff. Connected a OB2 Scan tool to see that it has a link error. Before I did the swap my civic has always been stuck in limp mode so we just reverted everything back to stock. Is it possible that the dash harness has something to do with this? And why is my civic running so bad? Before the swap I started up the same motor in the parts car and it ran fine but now it's questionable. Any ideas? Desperate for help. Btw it's manual and I swapped over the 2004 ecu.

 
Rep Power: 119

Oh holy snap dude..

So you also moved over the O2 sensors? 2002 and 2004 use different types.

 
Rep Power: 518

Still got the original engine? See if the alternator mounting bolts were loose.




Grounds, grounds, grounds

 
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I made sure the harness ground and the engine ground is connected

 
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Dude I know. It's terrible and yes I have swapped them over.

 
Rep Power: 518

9 times out of 10 when a PCM no longer communicates with a scanner, warning lights may be on, people say the relays click away behind the glovebox and power is severely restricted, it's found that the alternator mounting hardware had been loose at some point......... and the resulting 'runaway charging voltage' burned out the PCM.
Poor/bad ground cables for the drivetrain can cause the same issue

You've got a lot of swaparoo going on, I thought it was worth mentioning just because of your description.


There are some wiring differences between early and late, and vtec/non-vtec..both in the engine harness and the dash harnesses: AF sensor heater relay, and rear O2 sensor plug location immediately comes to mind...probably also some differences in ECM pinouts.

2001-03 used a regular O2 sensor in the primary location, 2004-05 use AF sensor in the primary location. They look about the same and do roughly the same job but electrically they are very different, their respective ECMs are very different, the sensors cannot be swapped as the ECMs have no idea what to do with the incorrect inputs..

I'd suggest you get a good set of wiring diagrams and research.

 
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Yes there is a clicking on the relays. They engines are both D17A1s the only thing I'm thinking of now is the dash harness and the alternator as you told me. But for sure the relays are clicking.

 
Rep Power: 518

The harnesses probably won't have anything to do with an ungrounded alternator and PCM burnout.

Something else people notice is the gauges are affected when the PCM loses its mind. 3 of the gauges are run by data coming from the PCM on a communication network, and once that data is corrupted the gauge cluster processor kinda goes stupid (coincides with loss of scanner communication).

Since we don't know how/when or if this current ECM is permanently damaged, I'm going to urge you to recheck the mounting bolts for the alternator, its mounting bracket, and engine/trans/chassis/battery grounds.

Once the PCM has lost its ability to communicate (data) with a scanner, most won't come back from that damage.


If you don't find and correct the root cause, it's doomed to repeat the failures and that gets expensive in a hurry